1. Technical Field
The present invention is directed to alkylaromatic sulfonates for enhanced oil recovery processes.
2. Description of the Related Art
Crude oil production from oil in subterranean reservoirs may involve use of various flooding methods as the natural forces that are used in the “primary recovery” process become depleted. A large portion of the crude oil may have to be driven out of the formation in “secondary” or “tertiary” recovery processes. In addition, some reservoirs may not have sufficient natural forces for oil production even by primary recovery processes. The production of crude oil using such flooding methods is one example of enhanced oil recovery process.
One trend in the petroleum industry now is to plan exploitation of the oil field at the beginning of the project. Injecting a displacing fluid or gas may begin early, long before the complete depletion of the field by primary recovery processes. Methods for improving displacement efficiency or sweep efficiency may be used at the very beginning of the first injection of a displacing fluid or gas, rather than under secondary and tertiary recovery conditions.
The least expensive and easiest method of flooding a subterranean reservoir 2 for the production of crude oil is by injecting a liquid or a gas into the well to force the oil to the surface. Water flooding is the most widely used fluid. However, water does not readily displace oil because of the immiscibility of water and oil and/or the high interfacial tension between the two liquids.
The addition of chemicals to modify the properties of the flooding liquid is well known in the art. Surfactants are one class of chemical compounds that have been used in aqueous media for enhanced oil recovery. Surfactants have been found to effectively lower the interfacial tension between oil and water and enabling the oil droplets to flow more easily through the channels of the reservoir.
Alkylaryl sulfonates have been used as surfactants for enhanced oil recovery. They have been used in surfactant flooding, alone, or in conjunction with co-surfactants and/or sacrificial agents. Alkylaryl sulfonates are generally used not only because they are able to lower the interfacial tension between oil and water, but also because when used in conjunction with varying amounts of sodium chloride they exhibit different phase behavior. At low salinity, alkylaryl sulfonates can have a tendency to stay in the aqueous phase, but at high salinity they tend to stay in the oil phase. Around mid-point salinity, a micro-emulsion forms in which appreciable amounts of oil and brine are in the micro-emulsion phase. It is at this mid-point salinity that the surfactant exhibits high oil recovery potential. The salinity of the water in subterranean hydrocarbon reservoirs may vary a great deal, for example, the Minas oil field in Indonesia has total dissolved salts of between 0.2 and 0.7 weight percent. Other reservoirs may have salinities as high as or higher than 2.0 percent sodium chloride and over 0.5 percent calcium chloride and magnesium chloride. It is desirable to optimize the alkylaryl sulfonates for surfactant flooding for enhanced oil recovery for a particular reservoir by determining the interfacial tension of the reservoir oil in an aqueous brine solution containing the alkylaryl sulfonates which matches the salinity of the reservoir water.
Generally, pure alkylaryl sulfonates, that is, those having a narrow range of molecular weights, are useful for recovery of light crude oils. Such alkylaryl sulfonates have been less useful for enhancing oil recovery of crude oils containing high wax content. Alkylaryl sulfonates having a broad spectrum of carbon chain lengths in the alkyl group are more desirable for use to recover waxy crude oils.
U.S. Pat. No. 6,989,355 discloses an under-neutralized alkyl-xylene sulfonic acid composition which contains a mixture of alkylated xylene sulfonic acids.
U.S. Pat. Nos. 7,332,460 and 7,468,343 disclose alkylxylene sulfonates and a method for recovering crude oil from a subterranean hydrocarbon containing formation using the alkylxylene sulfonates. The alkylxylene moiety in the alkylxylene sulfonate disclosed therein contains a high percentage of the 4-alkyl-1,2-dimethyl benzene isomer and a high percentage of alkyl group attachment to the xylene ring at positions higher than the 2-position on the alkyl carbon chain. In addition, the alkyl chain lengths comprise from about 40 to about 80 percent C12 to C20 and about 5 percent to about 15 percent of C32 to C58.
U.S. Pat. No. 7,495,140 (“the '140 patent”) discloses a process for alkylating an aromatic compound comprising (a) reacting a first amount of at least one aromatic compound with an amount of a mixture of olefins selected from olefins having from about 8 to about 100 carbon atoms, in the presence of a strong acid catalyst; and (b) reacting the product of (a) with an additional amount of at least one aromatic compound and an additional amount of a strong acid catalyst and, optionally, with an additional amount of a mixture of olefins selected from olefins having from about 8 to about 100 carbon atoms, wherein the resulting product comprises at least about 80 weight percent of a 1,2,4 tri-alkylsubstituted aromatic compound. Examples 1-3 of the '140 patent disclose alkylating o-xylene with a mixture of C14 to C30+ normal α-olefins wherein the mixture contained 8 wt. % C30+ olefins.
U.S. Pat. No. 7,449,596 discloses a process for preparing a synthetic petroleum sulfonate comprising (a) reacting at least one aromatic compound with a mixture of olefins selected from olefins having from about 8 to about 100 carbon atoms, wherein the mixture of olefins contains a distribution of carbon atoms that comprise from about 4 percent to about 15 percent C32 to C58, in the presence of an acidic ionic liquid catalyst, wherein the resulting product comprises at least about 50 weight percent of a 1, 2, 4 tri-substituted aromatic compound or a 1, 2, 3 tri-substituted aromatic compound or mixtures thereof; (b) reacting the product of (a) with sulfur trioxide, which has been diluted with air; and (c) neutralizing the product of (b) with an alkali or alkaline earth metal hydroxide.
It would be desirable to provide improved alkylaromatic sulfonates for enhanced oil recovery processes.